The FAA has received two reports indicating that, during modification of Boeing Model 747-200F series airplanes, fatigue cracking was found in the upper chord and web of the upper deck floor beams at body stations (BS) 340, 360, 380, and 400. One of these airplanes had accumulated approximately 19,100 total flight cycles, and the other approximately 18,500 total flight cycles. In addition, cracks were found at BS 380 on a 747-200F series airplane that had accumulated 11,586 total flight cycles. \n\n\tThe subject cracking was found in the upper chord of the upper deck floor beams, at the fastener location common to the fuselage frame inner chord. Cracks in this location are not detectable by visual inspection until the crack propagates to the horizontal flange of the chord. Analysis has demonstrated that, when a crack of the upper chord reaches the horizontal flange, the crack would propagate extremely rapidly, allowing little time to detect the crack prior to complete failure of the upper chord. \n\n\tThe upper deck floor beams are attached to the adjacent fuselage frames and provide a significant contribution to the structural integrity of the flat-sided fuselage. These floor beams also contain critical flight control cables and wire bundles that originate from the flight deck and flight engineer's control panel. The subject upper deck floor beams are made from 7075-T6511 aluminum, which is less durable and more susceptible to fatigue cracking than 2024 aluminum, which is used on passenger airplanes. Unsafe Conditions \\n\n\tFatigue cracking of the upper chord and web, if not corrected could result in failure of the upper deck floor beams and consequent damage to critical flight control cables and wire bundles that pass through the floor beams. Such damage could lead to uncommanded input to flight controls and reduced controllability of the airplane. \n\n\tIn addition, because the subject fatigue cracking has been found at multiple adjacent floor beam locations, failure of one floor beam could precipitate the failure of adjacent floor beams. Failure of these floor beams could cause the failure of the adjacent fuselage frames and skin, which could result in rapid decompression of the airplane.\n\n Similar Models \n\n\tBoeing Model 747-200C series airplanes have the same upper deck floor beam configuration to that on the affected Model 747-200F series airplanes. Therefore, both of these models may be subject to the same unsafe condition. \n\nExplanation of Relevant Service Information \t\n\n\tThe FAA has reviewed and approved Boeing Alert Service Bulletin 747-53A2420, dated March 26, 1998, which describes procedures for performing repetitive detailed visual inspections to detect cracks of the upper chord, web, and strap of the upper deck floor beams at BS 340 through BS 520 inclusive; and repair, if necessary. The alert service bulletin also describes procedures for a one-time open hole high frequency eddy current (HFEC) inspection to detect cracking at BS 340 through BS 420 inclusive, which would eliminate the need for the repetitive detailed visual inspections. \n\nExplanation of the Requirements of the Rule \n\n\tSince an unsafe condition has been identified that is likely to exist or develop on other airplanes of the same type design, this AD is being issued to prevent reduced controllability of the airplane and/or rapid decompression of the airplane due to fatigue cracking in the upper deck floor beams. This AD requires accomplishment of the actions specified in the alert service bulletin described previously, except as provided below. \n\nDifferences Between Rule and Alert Service Bulletin \n\n\tThis AD differs from the alert service bulletin in the following three respects: \n\n\t1. The alert service bulletin specifies that the manufacturer may be contacted for disposition of repair conditions. However, this AD requires the repair of those conditions to be accomplished in accordance with amethod approved by the FAA. \n\n\t2. The alert service bulletin requires a visual inspection of the upper deck floor beams at BS 460 and BS 480. This AD does not require inspection of this area because the upper chords of these floor beams are made from a 2024 material, which is more durable than the other upper deck floor beams and is less susceptible to the same type of fatigue cracking. \n\n\t3. The alert service bulletin does not require repeat detailed visual inspections or any open hole eddy current inspection of the upper deck floor beams at BS 440 through BS 520. For this area, this AD requires that the detailed visual inspection, if accomplished, be repetitively performed; and also requires that an open hole HFEC inspection eventually be accomplished. The floor beams at BS 440 through BS 520 (with the exception of floor beams at BS 460 and BS 480) are made from the same, less durable 7075-T6511 material and are subjected to the same operational loads as the floor beams withreported fatigue cracking; therefore, these beams are subject to the same type of fatigue cracking. Operators should note that procedures specified in Figures 2 and 4 of the alert service bulletin are identical. \n\nInterim Action \n\n\tThis is considered to be interim action. The manufacturer advises that it currently is developing a preventive modification that will positively address the unsafe condition addressed by this AD. Once this modification is developed, approved, and available, the FAA may consider additional rulemaking.\n \nDetermination of Rule's Effective Date \n\n\tSince a situation exists that requires the immediate adoption of this regulation, it is found that notice and opportunity for prior public comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days. \n\nComments Invited \n\n\tAlthough this action is in the form of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment on this rule by submitting such written data, views, or arguments as they may desire. Communications shall identify the Rules Docket number and be submitted in triplicate to the address specified under the caption "ADDRESSES." All communications received on or before the closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed. \n\n\tComments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the rule. All comments submitted will be available, both before and after the closing date for comments, in theRules Docket for examination by interested persons. A report that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket. \n\n\tCommenters wishing the FAA to acknowledge receipt of their comments submitted in response to this rule must submit a self-addressed, stamped postcard on which the following statement is made: "Comments to Docket Number 98-NM-127-AD." The postcard will be date stamped and returned to the commenter. \n\nRegulatory Impact \n\n\tThe regulations adopted herein will not have substantial direct effects on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government. Therefore, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment. \n\n\tThe FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and that it is not a "significant regulatory action" under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket. A copy of it, if filed, may be obtained from the Rules Docket at the location provided under the caption "ADDRESSES." \n\nList of Subjects in 14 CFR Part 39 \n\n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \n\nAdoption of the Amendment \n\n\tAccordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows: \n\nPART 39 - AIRWORTHINESS DIRECTIVES \n\n\t1. The authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. 106(g), 40113, 44701. § 39.13 (Amended) \n\t2. Section 39.13 is amended by adding the following new airworthiness directive: